<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            display: inline;
            /*在一行内显示,变成行内元素*/
            background-color: #f00;
            width: 100px;
            height: 100px;
            border: 1px solid black;
        }
        span{
            display: block;
            /*分两行显示,变成块级元素*/
            background-color: #f00;
            width: 100px;
            height: 100px;
            border: 1px solid black;
        }
        span{
            display: inline-block;
            /*变成块级或行内元素,依照你的标签而定*/
        }
    </style>
</head>
<body>
<!--
行内元素和块级元素没有太明显的界限,
可以通过display属性,将二者进行转换
-->
<div>
    aaaaa
</div>
<div>
    bbbbb
</div>
<hr>
<span>cccccc</span>
<span>dddddd</span>
</body>
</html>